Direct memory access control method, direct memory access controller, information processing system, and program

ABSTRACT

In a DMA control method in which a DMA controller transfers data in memory to an input/output device in accordance with the control information which is provided by a processing device to a DMA controller, a processing device implements a step in which the processing device sets an information block comprising the control information and the data in the memory; a step in which address information of the information block is provided by the processing device to the DMA controller; a step in which the DMA controller reads the information block from the memory based on the address information and extracts the control information; and a step in which the DMA controller transfers the data in the information block to the I/O device based on the control information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a direct memory access control technology, an information processing technology, and a program, and more specifically to an effective technology which applies to a direct memory access (DMA) technology, etc. in an information processing system which requires a high-speed data transfer.

2. Description of the Related Art

In a computer system, it is an important subject to implement data transfer effectively between memory and memory or between memory and an input/output device (I/O device) in order to improve the performance of the computer system. DMA is known as a method of solving this subject. (For example, refer to Patent Document 1)

An input/output (I/O) device transfers data to memory or receives data transferred from memory, and a storage device and an interface device are included in the I/O device. DMA is a mechanism in which dedicated hardware called a DMA control circuit controls data transfer based on instructions from a central processing unit (CPU) instead of the CPU controlling data transfer in the computer system.

In such a case, the CPU, memory and DMA control circuit are connected to one another via, for example, a memory hub, and the CPU, memory and DMA control circuit are supposed to transmit and receive data via this memory hub.

An instruction issued from the CPU to the DMA control circuit is called a descriptor, and a method by which the DMA circuit autonomously reads the descriptor from the memory and refers to the descriptor after the CPU prepares the descriptor in the memory has been widely used.

In other words, in a conventional method, apart from the data transferred by DMA to local memory under the control of the CPU, a descriptor in which control information (address of a transfer source, address of a transfer destination, transfer size, etc.) of DMA is included is developed.

When DMA is started by the CPU, the DMA circuit reads the descriptor and analyzes the control information, and transfers the data specified by the address of the transfer destination (local memory) to the I/O device by the data size designated by the descriptor.

As known from the above operation sequence, after the CPU prepares the descriptor and starts the DMA control circuit, the CPU can implement any other processing while data transfer is implemented, until DMA completion notification is provided to the CPU by an interrupt. Thus, the CPU is released from the comparatively simple process of data transfer and becomes available for more complicated processes, so that the performance of the system can be improved.

However, in the conventional DMA control technology in which a descriptor and data must be prepared separately in a memory, as described above, there are technical problems as follows.

In the case of the above conventional technology, in both “descriptor fetch” in which the DMA control circuit reads a descriptor and “data fetch” in which the DMA circuit reads data as the target of a DMA transfer, memory reading arises twice, and when reading such long data transfers that are generally implemented by DMA transfer are implemented in any interface via a memory hub, the overhead accompanied with data transfer becomes large because pre-fetch of the data is implemented in the memory hub.

Disclosed in Patent Document 1 is a technology which can change the functions of a DMA processing device by means of a program by associating each function of the DMA processing device with an instruction word, inputting a transfer processing procedure comprising an instruction word into a program storage area of the DMA processing device from outside, and implementing a transfer process in accordance with the function corresponding to the inputted instruction word, however, the aforesaid technical problems are not recognized in this technology.

Patent Document 1: Kokai (unexamined patent publication) No. 05-216808

SUMMARY OF THE INVENTION

The purpose of the present invention is to improve the efficiency in transferring data by DMA in an information processing system.

A first aspect of the present invention is to provide a DMA control method in which a DMA controller transfers data in memory to an input/output device in accordance with the control information which is provided by a processing device to the DMA controller, comprising:

a step in which the processing device sets an information block comprising the control information and the data in the memory;

a step in which address information of the information block is provided by the processing device to the DMA controller;

a step in which the DMA controller reads the information block from the memory based on the address information and extracts the control information; and

a step in which the DMA controller transfers the data in the information block to the I/O device based on the control information.

A second aspect of the present invention is to provide a DMA control method in which the control information includes the address of a transmission destination of the data and the size of the data in the DMA control method according to the first aspect.

A third aspect is to provide a DMA controller which transfers data in memory to an I/O device in accordance with control information provided by a processing device, including:

An address setting unit in which address information of an information block, including the control information and the data in the memory is set by the processing device;

A buffer in which part of the information block which is read from the memory and includes the control information is stored; and

A data transfer control unit which extracts the control information from the information block in the buffer and transfers the data included in the information block to the I/O device based on the control information.

A fourth aspect of the present invention is to provide an information processing system which comprises a processing device, memory, and a DMA controller which transfers data in the memory to an I/O device based on the control information provided by the processing device, wherein

-   -   the processing device includes control logic for implementing         the operation of setting an information block including the         control information and the data in the memory and the operation         of transmitting address information of the information block to         the DMA controller; and

the DMA controller reads the information block from the memory based on the address information transmitted from the processing device, extracts the control information included in the information block, and transfers the data included in the information block to the I/O device based on the control information.

A fifth aspect of the present invention is to provide a program which controls a processing device which causes a DMA controller to implement transfer processing, when transferring data from memory to an I/O device arises.

the operation of setting an information block including the control information and data which are required for the transfer processing in the memory; and

the operation of providing address information of the information block and starting the DMA controller.

According to the present invention, the DMA controller can acquire data to be transferred and control information required for the DMA transfer processing of the data, from the memory as an integrated information block in a single memory access, so that the time required for memory access can be made shorter than that of the conventional technology, in which control information and data are accessed separately. As a result, it is possible to improve the efficiency of transferring data by means of DMA in an information processing system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sequence showing an example of the operation of the information processing system which is an embodiment of the present invention.

FIG. 2 is a conceptual illustration showing an example of the configuration of an information block used for DMA in the information processing system which is an embodiment of the present invention.

FIG. 3 is a block diagram showing an example of the configuration of the information processing system which is an embodiment of the present invention.

FIG. 4 is a conceptual illustration showing an example of the configuration of a DMA controller included in the information processing system which is an embodiment of the present invention.

FIG. 5 is a flowchart showing an example of the operation of a DMA controller which is an embodiment of the present invention.

FIG. 6 is a sequence showing an example of the operation of the information processing system which is an embodiment of the present invention.

FIG. 7 is a flowchart showing an example of the operation of a CPU in the information processing system which is an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Described below are the details of the embodiment of the present invention with reference to the accompanying drawings.

FIG. 1 is a sequence showing an example of the operation of the information processing system which is an embodiment of the present invention. FIG. 2 is a conceptual illustration showing an example of the configuration of an information block used for DMA in the information processing system which is an embodiment of the present invention. FIG. 3 is a block diagram showing an example of the configuration of the information processing system which is an embodiment of the present invention. FIG. 4 is a conceptual illustration showing an example of the configuration of a DMA controller included in the information processing system which is an embodiment of the present invention. FIG. 5 is a flowchart showing an example of the operation of a DMA controller which is an embodiment of the present invention. FIG. 6 is a sequence showing an example of the operation of the information processing system which is an embodiment of the present invention. FIG. 7 is a flowchart showing an example of the operation of a CPU in the information processing system which is an embodiment of the present invention.

The information processing system 10 in this embodiment comprises a CPU (central processing unit) 11, memory 12, a DMA controller 13, and a memory hub 14, as illustrated in FIG. 3.

The DMA controller 13 is connected to an I/O device 20 via an I/O interface 15.

A program to be executed by the CPU 11 and data are stored in the memory 12, and the required information processing is implemented by the CPU executing this program.

When data transfer is required between the memory 12 and the I/O device 20, the DMA controller 13 processes the data transfer in place of the CPU 11 by the CPU controlling the DMA controller 13, as described later.

Hereinafter, data transfer processing which the DMA controller 13 implements between the memory 12 and the I/O device in place of the CPU 11 is referred to as DMA (direct memory access).

In this embodiment, a control program 12 a (control logic) in which the CPU 11 controls the DMA controller 13 to cause it to implement DMA is stored in the memory 12. This control program 12 a causes the CPU 11 to implement the processing shown in FIG. 6 and FIG. 7.

In this embodiment, the control program 12 a has the function of producing data 32 to be transferred and a descriptor 31 which is control information required for the DMA transfer control of the data 32 in the memory 12 as an information block, as shown in FIG. 2.

The control program 12 a provides the top address of this information block 30 in the storage area in the memory 12 (hereinafter referred to as an information block address 30 a) to the DMA controller 13 and causes the DMA controller 13 to implement DMA.

The DMA controller 13 in this embodiment comprises a memory interface 13 a, I/O interface 13 b, descriptor fetch circuit 13 c, descriptor buffer 13 d, state machine circuit 13 e, DMA start control register 13 f, data transfer control block 13 g, and DMA address pointer register 13 k (address setting unit), as shown in FIG. 4.

The memory interface 13 a is connected to a memory hub 14. The I/O interface 13 b is connected to the I/O device 20 via the I/O interface 15.

A DMA start command is set in the DMA start control register 13 f by the CPU 11.

The information block address 30 a indicating the storage position of the information block 30 in the memory 12 is set in the DMA address pointer register 13 k by the CPU 11.

The state machine circuit 13 e, when being started by the command set in the DMA start control register 13 f, controls the whole of the DMA controller 13 so that the block information 30 may be read from the area of the memory 12 which is specified by the information block address 30 a set in the DMA address pointer register 13 k.

The descriptor fetch circuit 13 c stores in the descriptor buffer 13 d the top portion of the information block 30 including the descriptor 31 out of the information block 30 which is read from the memory 12 via the memory hub 14 and the memory interface 13 a.

The state machine circuit 13 e extracts and analyzes the descriptor 31 included in the information block 30 stored in the descriptor buffer 13 d, and instructs data transfer to the data transfer control block 13 g, and upon receiving an instruction from the state machine circuit 13 e, the data transfer control block 13 g implements data transfer between the memory interface 13 a (memory 12) and the I/O interface 13 b (I/O device 20).

The data transfer control block 13 g comprises a memory transfer control circuit 13 h, a data buffer 13 i, and an I/O device transfer control circuit 13 j.

The memory transfer control circuit 13 h is initiated by the state machine circuit 13 e, and implements data transfer between the memory 12 and the data buffer 13 i via the memory interface 13 a.

The I/O device transfer control circuit 13 j is initiated by the state machine circuit 13 e, and implements data transfer between the data buffer 13 i and the I/O device 20 via the I/O interface 13 b.

In this embodiment, the descriptor fetch circuit 13 c stores in the descriptor buffer 13 d the top portion of the information block 30 including the descriptor 31 out of the information block 30 which is read from the memory 12 to the data buffer 13 i via the memory hub 14 and the memory interface 13 a.

In other words, when the information block 30 is read from the memory 12 to the data buffer 13 i via the memory interface 13 a, the top portion of the information block 30 including the descriptor 31 is stored in parallel in the descriptor fetch circuit 13 c.

Described below is an example of the operation of this embodiment.

When data in the memory 12 is transferred to an external I/O device 20 by means of DMA, as shown in FIG. 1, the CPU 11 which is controlled by the control program 12 a produces the information block 30 comprising the descriptor 31 and the data 32 and stores the information block 30 in the memory 12 (Step 201).

Then, the CPU 11 sets in the DMA address pointer register 13 k the information block address 30 a which is the top address in the storage area of the information block 30 in the memory 12, and starts the DMA controller 13 (Step 202) by writing a write command (a data transfer instruction from the memory 12 to the I/O device 20) to the DMA start control register 13 f.

The DMA controller 13 started by the CPU 11 accesses the memory 12 and reads the information block 30 (Step 203) based on the information block address 30 a set in the DMA address pointer register 13 k.

Then, the DMA controller 13 extracts the descriptor 31 from the read information block 30 and analyzes it (Step 204), and transfers data 32 to a target I/O device 20 specified by an I/O address 31 a (Step 205).

In this data transfer, when the processing of transfer data 32 of the size specified by a transfer data size 31 b is completed, the CPU 11 is notified of the completion of DMA, for example, by an interrupt (Step 206).

A detailed illustration of the operation of the DMA controller 13 at that moment is shown in the flowchart shown in FIG. 5. In other words, the DMA controller 13 monitors the DMA start control register 13 f and is on standby (Step 101), and when a write command is written from the CPU 11 to the DMA start control register 13 f, the DMA controller 13 reads the information block address 30 a from the DMA address pointer register 13 k (Step 102) and reads the information block 30 from the memory 12 based on this information block address 30 a (Step 103).

At that time, the information block 30 is read into the data buffer 13 i, and the descriptor 31 in the top portion of the information block 30 is read in parallel into the descriptor buffer 13 d by the descriptor fetch circuit 13 c.

The state machine circuit 13 e analyzes the descriptor 31 in the descriptor buffer 13 d, specifies information of the I/O address 31 a and the transfer data size 31 b (M) (Step 104), transfers the data 32 from the data buffer 13 i to the target I/O device 20 specified by the I/O address 31 a based on the I/O address 31 a and the transfer data size 31 b (Step 105, Step 106), and checks the transfer size (Step 107).

When the size N of the accumulated data which has already been transferred equals the size M of the data specified by the transfer data size 31 b, the state machine circuit 13 e transmits a transfer completion notification to the CPU 11 by interrupt, etc. (Step 108).

In the case of DMA from the I/O device 20 to the memory 12, processing illustrated in the lower part of FIG. 6 is implemented.

In other words, after the CPU 11 secures the storage area of the information block 30 in the memory 12 (Step 211), sets the transmission source address which specifies the I/O device 20 of the transmission source and the transfer data size 31 b, in the descriptor of the information block 30 and sets the information block address 30 a in the DMA address pointer register 13 k, the CPU 11 sets a read command (a data transfer instruction from the I/O device 20 to the memory 20) in the DMA start control register 13 f, and starts the DMA controller 13 (Step 212).

When the read command is set in the DMA start control register 13 f, the DMA controller 13 reads the descriptor 31 of the information block 30 from the memory 12 (Step 213), analyzes the descriptor 31 (Step 214), reads transfer data from the I/O device 20 to the data buffer 13 i (Step 215), and writes the transferred data to the data 32 area in the memory 12 (Step 216).

When the transfer is completed, the DMA controller 13 transmits a transfer completion notification to the CPU 11 by interrupt (Step 217).

The above described operation of the CPU 11 in the data transfer (write transfer) processing from the memory 12 to the I/O device 20, and in the data transfer (read transfer) processing from the I/O device 20 to the memory 12 is shown in the flowchart of FIG. 7.

First, the CPU 11 judges whether the data transfer is a write transfer (data transfer from the memory 12 to the I/O device 20) (Step 200), and if it is a write transfer, the CPU 11 stores the information block 30 in the memory 12 (Step 201 a). Then, the CPU 11 sets a transfer byte length (M) in the transfer data size 31 b of the descriptor 31 in the information block 30 (Step 201 b), and sets the I/O address 31 a which specifies the I/O device 20 of a transfer destination in the I/O address 31 a (Step 201 c).

Then, after the CPU 11 starts the DMA controller 13 (Step 202 b) by setting the information block address 30 a in the DMA address pointer register 13 k (Step 202 a) and setting a write command in the DMA start control register 13 f, the CPU 11 proceeds to another processing (Step 220).

When the CPU 11 judges that the data transfer is not a write transfer (but a read transfer), the CPU 11 secures an area for storing the information block 30 in the memory 21 (Step 211 a). Then, the CPU 11 sets the transfer byte length (M) in the transfer data size area 31 b in the area of the descriptor 31 in the storage area of the information block 30 (Step 211 b), and further sets the I/O address 31 a which specifies the I/O device 20 of a transfer destination in the area of the I/O address 31 a (Step 211 c).

Next, after the CPU 11 starts the DMA controller 13, by setting the information block address 30 a in the DMA address pointer register 13 k (Step 212 a) and setting a write command in the DMA start control register 13 f (Step 202 b), the CPU 11 proceeds to another processing (Step 220).

While the aforesaid “another processing” is being implemented, the CPU 11 receives a DMA completion notification from the DMA controller 13 by interrupt, etc., as described above.

According to this embodiment, the CPU 11 stores the data 32 and the descriptor 31 required to control the DMA processing of the data 32 in the information block 30, in the memory 12 as an integrated group, and reads this information block in a single read access from the DMA controller 13 to the memory 12, so that the occurrence of overhead when the descriptor 31 and the data 32 are read separately from the memory 12 can be avoided, and DMA processing from the memory 12 to the I/O device 20 can be effectively implemented in a short time.

Other DMA controllers in addition to interface devices and storage devices such as a magnetic disk device, optical disk device, magnet-optical disk device, and tape device can be connected to the DMA controller 13 in the information processing system as the I/O device 20.

A storage device is described as an example of the information processing system. The storage device comprises a memory shared by a plurality of access devices such as a host computer and a storage control device which controls data transfer between the memory and the access devices. In this case, the memory corresponds to the I/O device 20, and the storage control device corresponds to the information processing system 10. By applying the present invention to the storage device, the efficiency of data transfer from the storage device to the memory can be improved.

It is needless to say that the present invention can be changed within a range not exceeding its purport without being limited to the configuration shown in the above embodiment.

According to the present invention, it is possible to improve the efficiency of transferring data by means of DMA in an information processing system. 

1. A direct memory access (DMA) control method in which a DMA controller transfers data in memory to an input/output device in accordance with the control information which is provided by a processing device to the DMA controller, comprising: a step in which the processing device sets an information block comprising the control information and the data in the memory; a step in which address information of the information block is provided by the processing device to the DMA controller; and a step in which the DMA controller reads the information block from the memory based on the address information and extracts the control information. a step in which the DMA controller transfers the data in the information block to the I/O device based on the control information.
 2. The DMA control method according to claim 1, wherein the control information includes the address of a transmission destination of the data and the size of the data.
 3. The DMA control method according to claim 1, wherein the processing device, the memory, and the DMA controller transmit and receive information to and from one another via a memory hub.
 4. A DMA controller which transfers data in memory to an I/O device in accordance with control information provided by a processing device,comprising: an address setting unit in which address information of an information block including the control information and the data in the memory is set from the processing device; a buffer in which part of the information block which is read from the memory and includes the control information is stored; and a data transfer control unit which extracts the control information from the information block in the buffer and transfers the data included in the information block to the I/O device based on the control information.
 5. The DMA controller according to claim 4, wherein the control information includes the address of a transmission destination of the data and the size of the data.
 6. The DMA controller according to claim 4, wherein the DMA controller is connected to the processing device and the memory via a memory hub.
 7. An information processing system which comprises a processing device, memory, and a DMA controller which transfers data in the memory to an I/O device based on control information provided by the processing device, wherein the processing device includes control logic for implementing both the operation of setting an information block including the control information and the data in the memory and the operation of transmitting address information of the information block to the DMA controller; and the DMA controller reads the information block from the memory based on the address information transmitted from the processing device, extracts the control information included in the information block, and transfers the data included in the information block to the I/O device based on the control information.
 8. The information processing system according to claim 7, wherein the control information includes the address of a transmission destination of the data and the size of the data.
 9. The information processing system according to claim 7 which further includes a memory hub to which the processing device, the memory and the DMA controller are connected, wherein the processing device, the memory and the DMA controller transmit and receive information to and from one another via the memory hub.
 10. A signal which transmits a program for controlling a processing device which causes a DMA controller to implement transfer processing when the transferring of data from memory to an I/O device arises, wherein the processing device is made to implement the operation of setting an information block including the control information and data which are required for the transfer processing in the memory; and the operation of providing address information of the information block and starting the DMA controller.
 11. The signal transmitting a program according to claim 10, wherein the control information includes the address of a transmission destination of the data and the size of the data. 